1. Field of the Invention
This invention relates to a polyurethaneurea solution that is protected against changes in viscosity and to spandex dry spun therefrom. More particularly, the invention concerns such a solution containing a small amount of a specific 4,4'-biphenylene diphosphonite.
2. Description of the Prior Art
Polyurethaneureas are prepared by reacting a hydroxyl-terminated linear polymer, such as a polyether glycol or a polyester glycol, with an organic diisocyanate to form a prepolymer, which is then chain-extended with a diamine. Usually, the reactions are conducted in an inert organic solvent. The solutions are suited for dry spinning into spandex. However, to produce spandex with consistent properties, the solutions should be of constant viscosity. Fluctuations or changes in solution viscosity during storage, processing or dry spinning can result in variations in threadline tension, difficulties in winding and unwinding, and various non-uniformities in elastic properties of the spandex.
Several methods have been suggested to control polyurethaneurea solution viscosity. However, each has shortcomings. For example, Nakahara et al, U.S. Pat. No. 3,726,836 discloses use of an N,N-dialkylhydrazine as a polymer chain terminator and subsequent heat-aging to stabilize polyurethane solutions against gelation. However, such chain terminators are potentially carcinogenic and the process is time-consuming. Also, Schollenberger et al, U.S. Pat. No. 3,939,111 discloses use of ammonium salts of strong acids to stabilize polyurethane solution viscosity, but such salts are hygroscopic and the presence of water in the polymer solution can render the solution unsatisfactory for dry-spinning. Accordingly, a purpose of this invention is to provide polyurethaneurea solutions of constant viscosity, so that the solutions can be dry spun into spandex, without suffering the aforementioned shortcomings.
Lewis, U.S. Pat. No. 4,548,975 in Example 3, Comparison 9, and Kausch et al, U.S. Pat. No. 4,877,825, Comparison Example 13, each disclose a polyurethaneurea solution containing tetrakis-(2,4-di-t-butylphenyl)-4,4'-biphenylene diphosphonite in an amount that results in a 2% concentration of the phosphonite in dry-spun spandex. The disclosures concern protection of spandex against discoloration due to heat, combustion gases and light. However, in both references the phosphonite is employed in comparison samples that are shown to be inferior to the claimed stabilizers of the references. Furthermore, both references are silent on the problems of changes in polymer solution viscosity.